In certain laboratory chemical processes small compact valves are desirable which are capable of handling fluids which may react upon metals and elastomeric O-ring materials. For example, present methodology in peptide synthesis demands that metering and reaction vessel valves handle material such as methylene chloride, trifluoroacetic acid, dioxane 4N HC1, triethyl amine and dimethyl formamide. For this use glass or ceramic ball valves of the type heretofore available with seats composed of polytetrafluoroethylene are too large. Such valves require ball to stem floating connections and the design cannot be reduced to scale because of the strength problems at the ball to stem floating connection. Small ball valves with integral stems have been invariably composed of metal. The substitution in conventional ball valve designs of nonmetallic materials such as a fluorocarbon product sold under the trademark, Kel-F, glass or ceramic for metal is impractical because of over constraint due to the stem packing gland.
Nevertheless ball valves have certain inherent advantages such as ease with which perfect spheres can be generated and the fact that a free-floating ring will mate perfectly with a sphere and that the wear form of a circular ring and a sphere is, in turn, a circle and a sphere. It is desirable, therefore, that a ball valve be so arranged that the seats and the ball are free to rotate optimally for seating and operation. The freedom of seating is lost with an integral stem ball valve in that the ball is constrained by the packing against the stem.
It is accordingly an object of the invention to provide a construction in which the stem packing is replaced by a circular ring bearing against the sphere so that it will have the same advantageous location and wear characteristics enjoyed by the seats of conventional ball valves.
A further object of the invention is to locate the ring seats and ring seals for the valve stem so that forces on the ball are balanced with the loads on the rings centered and intersecting at the center of the sphere.
A still further object of the invention is that the seats and stem seals and associated parts be identical for the inlet and outlet openings and for the stem seal.
Still another object of the invention is to obtain the advantages of a ball valve in a small size composed of materials which are resistant to active chemical reagents.
The invention also has for its object the complete separation of reinforcing ring and pressurizing threads from the flow path, symmetrical and uniform distribution of sealing forces, self-alignment of the valve seats in accordance with a floating-ring principle, elimination of leakage paths and employment of one-piece seal and tube connector fittings, reduction of dead volume to a minimum, and relative simplicity of parts.
Other and further objects, features and advantages will become apparent as the description proceeds.